U.S. Pat. No. 2,759,106 issued to Wolter discloses an image forming mirror system that utilizes nearly grazing incidence of X-rays for use in X-ray microscopy. Based on the work done by the patentee, high resolution, glancing incidence X-ray telescopes have been built and flown on numerous sounding rockets and satellites. One of the most popular designs is the so called Wolter I configuration which utilizes coaxial, common focal, internally reflecting, paraboloidal and hyperboloidal mirrors. In this configuration, relatively soft, substantially on-axis X-rays incident on the mirrors are converged at the prime focus of the telescope where a detector, sensitive to relatively soft X-rays, detects the glancingly reflected converged X-rays.
Glancing incidence X-ray mirror systems are highly effective over the soft x-ray/extreme ultra-violet (XUV) wavelength range from about 3 Angstroms to about 600 Angstroms producing high resolution focused images allowing the use of small low background detectors with extremely high signal-to-noise ratios. Below about 3 Angstroms, very small glancing angles are required, which means that very great focal lengths are necessary; and the collecting area becomes very small for a system of reasonable diameter. Consequently, glancing incidence X-ray mirror systems are not suitable for imaging hard X-rays and gamma rays.
In 1968, R. H. Dicke proposed an important technique for imaging hard X-rays. This technique involves the use of a plate opaque to hard X-rays pierced with a random ray of pinholes which produces an array of overlapping images at the focus plane. By knowing the configuration of the pinhole array, the many overlapping images can be deconvolved into a single useful image by either holographic methods or by digital processes utilizing a computer. This approach affords the advantage of the resolution of a single small pinhole coupled with the much larger collecting area made possible by the use of many apertures. When large separation distances between the multiple pinhole mask and the detector are used, superb resolution (i.e., about 0.1 seconds of arc) can be achieved for X-rays in the energy range from 1-100 KEV.
A simple random array of pinholes will function adequately under some conditions, but this is not the best type of coded aperture system. More sophisticated aperture systems are based upon the Hadamard matrices and offer the advantage of very flat sidelobes in the reconstructed image. Uniformly redundant arrays, described by E. E. Fenimore and T. M. Cannon, have autocorrelation functions with perfectly flat sidelobes and combine the advantages of the random array (i.e., high transmission characteristics) with those of the non-redundant pinhole arrays (i.e., flat sidelobes). Such approach permits the use of a smaller detector than required by the random array and yet allows imaging of low intensity, low contrast sources. A further increase in resolution at some loss in sensitivity can be achieved by the introduction of one or more coded aperture masks in front of the detector as described by R. B. Hoover and J. H. Underwood in U.S. Pat. No. 3,749,911.
In the past, it has been conventional to use one or the other of the two types of X-ray telescopes described above for separate investigations of relatively soft X-ray sources as well as relatively hard X-ray sources. An X-ray telescope system capable of simultaneously producing high resolution images in both the hard and soft X-ray regions would be ideally suited for imaging hard X-ray observation of emission associated with the impulsive phase of flares, coronal transients, and shock waves with precisely simultaneous high resolution images of the parent flare and associated loop systems at soft X-ray wavelengths in order to provide important new insights into the nature and characteristics of solar x-ray/XUV phenonmena. It is therefore a primary object of the present invention to provide a new and improved X-ray telescope which provides for simultaneously imaging soft and hard X-rays.